The Key:
(C)at
(D)re
(E)mi
(F)fu
(G)so
(A)la
(B)sy
For the “i” in words like “him, “this” etc, the “i” is pronounced as the “ee” in (E)mi.
For the “i” in words like “first” and “thirst” or for words with the sound of “earth” you use the “(D)re” note (even though it is a completely different sound) it serves both purposes. It can be remembered by how it looks in reverse (erd).
The last letter (B) is for words which use the letter "Y" and have the "EE" sound, while the third letter (E) is for words which have the "EE" sound without the letter "Y".